1. Field of the Invention
The present invention relates to building construction, and more specifically, to apparatus for anchoring walls to foundations and lower floors.
2. Background
Strong winds and earthquakes subject walls and others elements of a building to tremendous forces. If these forces are not distributed to the proper elements or structures capable of withstanding such force, the building may be torn apart. Foundations are often the strongest element of a building. Securely tying the walls of a building to the foundation greatly improves structural performance during periods of strong wind or earthquake. Securement promotes single body motion and limits whiplash amplification that often results in structural failure.
Under extreme conditions, a building may be violently loaded or shaken back and forth in a lateral (side to side) direction. If a shear wall is tightly restrained at its base, loads may be smoothly transferred to the foundation. The loads may then be resolved in the foundation, where they appear as tension and compression forces.
Buildings are often composed of long walls, (walls with a length greater than the height) and short walls (walls that have a length shorter than the height). The tendency for a wall to lift vertically off a foundation is inversely proportional to the length of the wall. Tall narrow shear walls, which may be found in nearly all homes, act as lever arms and may magnify an imposed load. In certain instances, the actual load on the securement system may be magnified to several times the originally imposed load.
Wall securement may prevent lateral and vertical motion between the walls and the foundation. Additionally, it may be necessary to support the wall against forces that would tend to distort the wall""s general rectangular shape. Building codes often require external and load bearing walls to be shear resistant by providing a plywood plane to support shear forces that may be imposed on the wall. Many times, building codes also require lateral and vertical securement of a wall to the foundation. Lateral and vertical securement may be accomplished by employing hold-downs, also referred to as tie-downs.
Typically, hold-downs are attached eccentrically, spaced from the neutral axis, on a selected number of support members (e.g. posts, beams, or studs) which make up the wall of building. Eccentric attachment introduces a moment in the support member that greatly reduces the tensile capacity thereof. Eccentric attachment may also cause the support member to deflect excessively. The tensile force caused by tightening the hold-down may cause the support member to bow. Bowing tends to promote column buckling and reduces the effectiveness of the support member to provide sufficient structural support.
Moreover, hold-downs are difficult to install and expensive to fabricate. Accordingly, a need exists for a balanced hold-down that may be easily installed. It would be a further advancement to provide a balanced hold-down that may be produced in greater quantities with greater speed and less expense.
It is an object of the present invention to provide a balanced hold-down that may be easily and quickly secured to support members.
It is a further object of the present invention to provide a hold-down that may be mass produced inexpensively.
In certain embodiments, an apparatus and method in accordance with the present invention may include a hold-down for securing first and second support members to an anchoring device in a balanced manner. The anchoring device may extend from a foundation or from a wall up through a floor to another wall positioned thereabove. When an anchoring device extends through a floor, hold-downs in accordance with the present invention may be used to engage and secured both ends thereof.
A hold-down in accordance with the present invention may have a first flange, a second flange, and a base connecting the first and second flanges and having an aperture for admitting an anchoring device. The first and second flanges may engage first and second support members respectively. The first and second flanges may each have multiple securement apertures. The securement apertures may allow a securement mechanism to be introduced therethrough to engage the first or second support member or both. In certain embodiments, the securement mechanism may be a nail. The securement mechanisms may be admitted into the support members in a manner selected to substantially reduce splitting of the support member. The number of securement apertures and accompanying securement mechanisms may be selected to provide sufficient engagement to meet or exceed a minimum strength requirement. The minimum strength requirement may be selected to meet a given building code.
A hold-down in accordance with the present invention may be loaded in tension when in use. Tensile loading may permit a hold-down to be formed of a relatively thin material (e.g. sheet metal). A hold-down that may be loaded in compression will likely be made of a relatively thick material. The thicker material may be needed to resist buckling as well as the applied load. A hold-down loaded in tension may only need to resist the applied load. As a result, a hold-down to be loaded in tension may be lighter, more easily manufactured, and cheaper than a hold-down to be loaded in compression.
In one embodiment, the hold-down is installed by securing the first flange to a first support member and securing the second flange to a second support member. An anchoring device may be admitted through an aperture provided in the base. A fastener may be tightened on the anchoring device to load the first and second flanges in tension.
In certain embodiments, the base may be formed to resist distortion or failure thereof during installation and the subsequent loading that may be experienced during strong winds, earthquakes, and the like. The base thickness may be selected to resist distortion and unwanted flexing. Additionally, the base may be formed in a manner to increase the section modulus thereof. Distortion and unwanted flexing of the base may also be substantially reduced by positioning an insert, having the strength and rigidity needed to resist the forces of use, over the base.
In certain applications, selected embodiments in accordance with the present invention may provide a hold-down for engaging first and second support members having rectangular cross-sections. Such rectangular support members may each have an inside face, outside face, left side, and right side. The first and second support members may be arranged so that inside faces face each other. In such a configuration, the first flange may be secured to the inside face of the first support member while the second flange may be secured to the inside face of the second support member. In another embodiment, the first flange may be secured to left and right sides of the first support member while the second flange may be secured to left and right sides of the second support member.
Securement mechanisms may be introduced through securement apertures of each flange at any suitable angle with respect to the surface to which the given flange is being secured. The angle at which the securement mechanism is introduced may be selected to mitigate the risk of splitting the support member. In certain embodiments, the first and second flanges may be formed in a manner to provide a flat, parallel surface to facilitate introduction of the securement mechanism into the support member at an angle other than normal and to contact a head of the securement mechanism.
In some applications, the outside faces of the first and second support members may be inaccessible. Certain embodiments in accordance with the present invention allow for the securement mechanisms to be introduced through the first or second flange and into the first or second support member without access to the outside faces of either support member. Additionally, the hold-down may be formed to allow the securement mechanism to be installed from a location that is not collinear with the first and second support members.
A method for fabricating a hold-down is also included within the scope of the present invention. The method of fabrication may include cutting a blank, such as a selected shape of sheet metal, to sustain forming into a first flange, a second flange, and a base. The first and second flanges may have securement apertures extending therethrough. The blank may be formed or bent to position the first and second flanges substantially parallel to one another with the base connecting the first flange to the second flange, permitting the first and second flanges to engage a first and a second support member in a balanced manner.
Consistent with the foregoing objects, and in accordance with the invention as embodied and broadly described herein, an apparatus and method are disclosed in suitable detail to enable one of ordinary skill in the art to make and use the invention. The features, and advantages of the present invention will become more fully apparent from the following description, or may be learned by the practice of the invention as set forth hereinafter.